At the equator, 360 degrees corresponds to 25,000 miles of longitudinal distance, so 1 degree = 69.4 miles. That means 0.000001 degree corresponds to 0.367 feet. GPS receivers typically self-report accuracies of a few feet, so entering coordinates to more than 5 decimal places is probably pointless.

Just a data point, but my geocache software on my phone reports to three decimals of minutes and self reports and accuracy of 16 feet. It’s enough to get one close but not so close that you don’t have to search for the cache.

Up/down rounding is more accurate. Errors just add together, (that is two errors cannot be assumed to cancel out !)

Just ignoring the final digit means wiping 9 off ?

0-4 means 0, which you ignore .

5 - 9, means add one to the column to the left (with carry as appropriate)
In this case, the maximum error introduces is 5… half that of if you just drop the last digit.

An even better method (even though only slightly better I’m nitpicking here) is to round down 0-4, round up 6-9, and to use a random algorithm to decide what to do with 5. Always rounding up fives introduces a slight upward bias, meaning that over the long run you will round up more than you round down, so errors won’t cancel out. A typical random algorithm would be to say that you always round to the even figure. So 47.5 would be rounded up to 48 (because the 8 is even, the 7 is not), whereas 42.5 would be rounded down to 42. This preserves symmetry; over the long run, you round down just as much as you round up.